Method and system for amplifier control

ABSTRACT

A method is disclosed wherein a power level indicating a level of transmission power from an amplifier is provided. An indication of at least one of channel, channel bandwidth, OOB spectral requirements, spectral mask requirements, EVM, modulation rate, and modulation type is also provided. A control signal for controlling one of a bias current provided to the amplifier and a matching circuit for matching an output port of at least a stage of the amplifier is generated, the control signal determined in dependence upon the power level and the at least an indication. Then the one of the bias current and the matching circuit is adjusted in accordance with the control signal.

FIELD OF THE INVENTION

The invention relates generally to RF amplifiers and more particularlyto an amplifier and method having a dynamically adjustable bias forimproving amplifier efficiency.

BACKGROUND

Traditionally, a semiconductor RF signal power amplifier (PA) is biasedwith VCC voltage or VDD voltage along with base or gate voltage toestablish an operating point for an amplifying transistor or transistorarray. In the context of a bipolar transistor, the base voltage orcurrent is established using a bias circuit that is designed to supply abias point. As is well known in the art, the bias point determines manyof the amplifying characteristics of the transistor. In fact,classification of amplifiers into class A, class B, class AB, etc. isprimarily determined by the bias point.

Power amplifiers, particularly those based on semiconductor transistors,usually comprise one or more stages of amplification. For example, afirst stage of amplification might receive a native RF signal andamplify that signal to a level suitable for a second stage. Typically,three stages of amplification are used in an amplifier suitable for802.11a, 802.11b, 802.11g, 802.16e, and other wireless standards inorder to provide 25 to 35 dB of gain. Great care is taken to set theoperating point for each stage of amplification—for each transistor inthe chain—such that an optimum gain and linearity are established foreach stage, and the complete PA operates in a harmonious manner. Forexample, the first stage could provide 10 dB of gain, the second stageis biased to provide only 5 dB of gain, and a third and final stageprovides 15 dB of gain resulting in a 30 dB amplifier. In addition to anoperating point for each transistor in the amplification chain, thematching circuit between transistor amplification stages is designed andmanufactured such that an efficient transfer of signal power issupported from stage to stage.

Adjustment of the bias point is a mechanism for amplifier control. Inprior art circuits, adjustable bias circuits are provided to allow forcircuit tuning—correction of bias current variability caused, forexample, by manufacturing inaccuracies. It is well appreciated in theart of amplifier design, that through the operating point, theamplifying qualities of the semiconductor transistor are adjustable suchthat more or less gain is provided, more or less distortion ismanifested, or quite simply more or less current consumption occurs atthe operating point. Thus, even within the strict tolerances ofsemiconductor manufacturing, small post production tuning of a fixedbias may result in significant improvement of the amplifier operation.

Adjustment of the interstage matching circuit is another mechanism foramplifier control. In fact, the matching circuit following the outputport of the final stage of amplification is very important in that itmatches an output signal from the amplifier to an antenna or load. Amechanism to control the matching circuit at the output port may permitmatching for variations in load and protection of semiconductortransistors from large mismatch effects. Thus, for example, externalmatching circuits as manifested using the placement of L, R, and Ccomponents on a printed circuit board are often used to ensure accurateimpedance matching between an amplifier and a load.

The operating point and matching circuit deterministically result in aPA providing an amplified RF signal with certain qualities. For examplein typical applications, an amount of distortion and power level are twoqualities that must be compliant with certain standards established bygovernmental regulators and/or interoperability committees which havethe mandate to certify products as compliant. For example, the IEEE802.11g standard requires certain qualities in respect of the spectraloutput of the RF transmission system (Mask) such that signal energy incertain bands is below both relative and absolute threshold values.Moreover, users of such transmission systems are expecting signalclarity resulting from a low probability of transmission error and a lowpacket error rate. In this respect, error vector magnitude (EVM) as apercentage is used as a figure of merit for signal clarity. For example,a 3% EVM specification might be expected or required from thetransmission system in order to achieve a requisite de minimis packetrate. Both compliance with the Mask and EVM are determined by the RFsignal quality at an output port of the amplifier, which in turn isdetermined by the operating point, matching circuit and other settings.Thus, during manufacture or assembly, the EVM is determinable and thosetunable portions of the circuit are adjusted to provide a desired EVMand then fixed for the circuit to ensure EVM compliance.

Moreover, it should also be understood that the Mask might vary fromjurisdiction to jurisdiction. For example, Mask requirements in Japanare different from those in Europe or North America. Even allowablein-band power output levels might be different in each jurisdiction andexpectations in respect of EVM also vary from user to user of thetransmission system. A universal goal however, exists from user to userand from jurisdiction to jurisdiction—that is, low power consumption andhigh power efficiency. Low power consumption will provide the user of aportable transmission device, such as a cell phone, with a long periodof usage between charging times. High power efficiency provides the userwith less waste of operating energy in the transmission device—gettingthe most out of the available battery energy. Such waste often manifestsas heat generation, which must be dealt with and dissipated. Clearly,using battery power in a wasteful manner is not conducive to long ‘talktime’ in the context of a portable transmission device and generatingexcess heat is not conducive to comfort if, for example, a batteryoperated device were to heat up.

A well known trade-off between linear performance (low EVM andcompliance with Mask) in an amplifier and power consumption exists. Anamplifier can be biased such that it provides very linear amplificationperformance (low signal distortion) but only at the cost of high powerconsumption. Therefore, by knowing in advance the linearityrequirements, a designer can approximately optimize power consumption toprovide just enough linear performance whilst minimizing powerconsumption.

Traditionally, the operating point and the interstage matching circuitsare established and fixed by design. Clearly, if the operating point foreach transistor amplifier is fixed at the time of manufacture then anoperating point that provides for the most stringent requirements isfixed and the transmission system has no flexibility to adjust bias ormatch in the context of a varying linearity or power output requirement.Since many country markets (also known as operating jurisdictions) havedifferent requirements, either some of those operating jurisdictions areserviced with devices have less efficient battery usage than is possibleor use devices that are customized for those markets. This is clearlyless than ideal and it would be efficient to be able to manufacturedevices that are capable of serving more than one operationaljurisdiction whilst being compliant with the different requirements ofthat jurisdiction.

In the context of wireless LAN (WLAN) Power Amplifiers (PAs) operatingunder one of the IEEE 802.11 standards, PAs are typically biased andoptimized for best EVM performance at a specified output power.Moreover, the transmit power level for higher modulation rates may beEVM limited depending upon the PA design. As modulation rates aredecreased, transmit power can be increased until Mask or Band Edgeperformance limits the transmit power.

In addition, WLAN PAs are typically designed for class AB operation withfixed bias currents for each individual amplifier stage. Someapplications permit the reduction of transmit power to reduce DC powerconsumption and improve battery life for portable applications. However,simply reducing the transmit power level is inefficient. For example, ifthe specified performance of the power amplifier is 3% EVM at 20 dBmoutput power, then backing off the transmit power to 10 dBm will resultin very good EVM and Mask performance but at much reduced efficiencybecause the amplifier is biased to provide a much higher level of linearoutput power. In contrast, reducing the bias at lower transmit powerwill drastically improve efficiency and greatly improve battery life.

In AGC design it has been proposed in U.S. Pat. No. 6,763,228 to use afeedback system for controlling bias. The system aims to achieveautomatic gain control through bias control, which is achievable sinceit is known to use bias to control amplifier gain. In U.S. Pat. No.6,873,211, bias is used to switch an amplifier between a linear mode ofoperation and a saturated mode of operation. Each of these bias controlmethods addresses an issue relating to controlling amplification of theamplifier—the bias is changed to control the amplifier's gain—and iscontrolled in dependence upon gain characteristics of the amplifier.

Further, for RF PAs operating in the range of 2.4 to 10 GHz, digitalcontrol is not typically used. These PAs are often based onsemiconductor technology platforms such as the Gallium Arsenide (GaAs)compound, which do not feature complementary logic devices and, as such,do not receive or logically manipulate digital signals. In fact, whencontrol signals are required, GaAs PAs work with analog control signals.Further, these same PAs are precluded form working with digital signalsespecially at lower voltages (e.g. 2.5V, 1.8, 1.2V logic).

It would be advantageous to provide an amplifier and method forimproving battery life by improving amplifier efficiency in the contextof a variety of operational jurisdictions while maintaining otheroperating characteristics of said amplifier.

SUMMARY OF EMBODIMENTS OF THE INVENTION

In accordance with the invention there is provided a method comprising:providing a power level indicating a level of transmission power from anamplifier; providing at least an indication of at least one of channel,channel bandwidth, OOB spectral requirements, spectral maskrequirements, EVM, modulation rate, and modulation type; and, providingat least a control signal for controlling one of a bias current providedto the amplifier and a matching circuit for matching an output port ofat least a stage of the amplifier, the control signal determined independence upon the power level and the at least an indication; and,adjusting the one of the bias current and the matching circuit inaccordance with the control signal.

In accordance with another embodiment of the invention there is providedan amplifier circuit comprising: an amplifying transistor for receivingan input RF signal and for providing an output amplified RF signal, theamplifying transistor for receiving a bias current; and, a controlcircuit for determining a first bias current for the amplifyingtransistor and for providing a control signal in dependence thereon, thefirst bias current determined in dependence upon an error vectormagnitude (EVM) target and an operating point of the amplifier circuit,the first bias current determined for improving the overall amplifierefficiency of operation relative to an amplifier with a fixed biascurrent.

In accordance with another embodiment of the invention there is providedan amplifier circuit comprising: an amplifying transistor for receivingan input RF signal and for providing an output amplified RF signal, theamplifying transistor for receiving a bias current; and, a controlcircuit for determining a first matching condition for the amplifyingtransistor and for providing a control signal in dependence thereon, thefirst matching condition determined in dependence upon an error vectormagnitude (EVM) target and an operating point of the amplifier circuit,the first matching condition determined for improving the overallamplifier efficiency of operation relative to an amplifier with a fixedmatching condition.

In accordance with another embodiment of the invention there is providedan amplifier circuit comprising: an amplifying transistor for receivingan input RF signal at a frequency above 2 GHz and for providing anoutput amplified RF signal, the amplifying transistor for receiving abias current; and, a control circuit for determining one of a first biasand a first matching condition for the amplifying transistor and forproviding a digital control signal in dependence thereon, the one of afirst bias and a first matching condition determined in dependence uponother than merely a linearity of gain of the amplifier and an operatingpoint of the amplifier circuit, the one of a first bias and a firstmatching condition determined for improving the overall amplifierefficiency of operation relative to an amplifier with a fixed one of afirst bias and a first matching condition.

In accordance with another embodiment of the invention there is provideda method comprising: providing a power level for transmission from anamplifier of a mobile device; providing at least an indication of astandard within which the amplifier is to operate, the standarddifferent for different locations of operation of the mobile device;and, providing at least a control signal for controlling one of a biascurrent provided to the amplifier and a matching circuit for matching anoutput port of at least a stage of the amplifier, the control signaldetermined in dependence upon the at least an indication of a standardand for improving operating efficiency of the mobile device for thestandard relative to operating efficiency of the mobile device acrossthe different locations; and, adjusting the one of the bias current andthe matching circuit in accordance with the control signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described inconjunction with the following drawings, in which:

FIG. 1 a is a simplified flow diagram of a method according to anembodiment of the invention;

FIG. 1 b is a simplified block diagram of an amplifier circuit accordingto an embodiment of the invention;

FIG. 2 a is a graphical representation of EVM and Mask Limit vs. Pout;

FIG. 2 b is a graphical representation of EVM vs. power output at twodifferent bias points;

FIG. 3 is a graphical representation of total current vs. power output;

FIG. 4 is a graphical representation of Digital Bias Optimized for 3%EVM;

FIG. 5 is a graphical representation of Current Drain for Optimized 3%EVM;

FIG. 6 is a graphical representation of Efficiency optimized forSpectral Mask;

FIG. 7 is a graphical representation of 802.11b 1 Mbps OOB performance;

FIG. 8 is a graphical representation of 802.11g 54 Mbps OOB performance;

FIG. 9 is a graphical representation of Current Drain increase forOptimum OOB;

FIG. 10 is a graphical representation of burst current vs. output power;

FIG. 11 is a graphical representation of EVM vs. output power;

FIG. 12 a is a simplified flow diagram of a method relying on a discretenumber of biasing states for the amplifier; and

FIG. 12 b is a simplified block diagram of an amplifier for use with themethod of FIG. 12 a.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The following description is presented to enable a person skilled in theart to make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the scope ofthe invention. Thus, the present invention is not intended to be limitedto the embodiments disclosed, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

In table 1, System EVM requirements are shown for different modulationrates. As is evident, different modulation schemes and rates have verydifferent EVM requirements and designing to meet these requirementsoften requires a design that meets the most demanding of therequirements. Often, this limits the power consumption advantages ofusing other modulation schemes or rates since the system is lessefficient when operating at modulation schemes and rates other than thathaving the most demanding requirements. Hereinafter, modulation schemesor rates for which some standard has defined demanding EVM requirementswill be referred to as demanding modulation schemes or rates. Of course,designing the system to be more efficient with less demanding modulationschemes or rates is also ineffective because (a) it only aggravates thedrawbacks to the more demanding modulation schemes and (b) often itresults in the failure to meet specification requirements for those moredemanding modulation schemes or rates. For example, a PA may be designedwith a very high linearity performance with a view to the requirement ofa data rate equal to 54 Mbps. Operating such a PA at lower data rateswould normally be wasteful of the power consumption if the bias pointcould not be adjusted to a less linear regime of operation for the PA.

TABLE 1 802.11g System EVM requirements Modulation rate (Mbps) EVM (dB)EVM (%) BPSK 6 −5 56.2% BPSK 9 −8 39.8% QPSK 12 −10 31.6% QPSK 18 −1322.4% 16-QAM 24 −16 15.8% 16-QAM 36 −19 11.2% 64-QAM 48 −22 7.9% 64-QAM54 −25 5.6%

A PA with fixed bias points and fixed interstage/output port match has afixed power consumption, heat dissipation, and linearity performance onall channels, regardless of actual requirements or use. In the contextof multi-mode operation, such a PA cannot adjust the operating point ormatching circuits to decrease or increase linear performance as requiredby the mask requirements, EVM requirements, or jurisdiction-dependentoperating specifications.

A PA's operating efficiency is beneficially enhanceable by approximatelyoptimizing a trade-off between the PA's efficiency and linearity by aset-up of its operating point and matching circuit based on thede-minimus mask and EVM requirements for the modulation scheme and rateof a channel that is to be used in a multi-channel OFDM system. Such anapproach maintains the specified EVM performance but reduces powerconsumption. Controlling the PA's bias provides a straightforward methodfor approximately optimizing performance as the modulation rate, maximumallowed power level, or in-band channel is changed.

In a broad embodiment, in accordance with system requirements or userdemand, a baseband processor determines one or more of EVM, mask,channel to be used, maximum allowable power output level, modulationtype, and data rate associated with the RF output signal to betransmitted. The baseband processor then maps this information onto adigital control instruction for the PA. The PA then adjusts, in apredetermined manner, the operating point for one or more amplificationstages and/or the matching circuit adjustments for one or more of theinterstage/output match circuits. The resulting operating point andmatching circuit configuration is one that represents a better trade-offin efficiency whilst meeting the requirements of the system effectively.Some possible requirements include EVM, mask, channel to be used,channel bandwidth, maximum allowable power output level, modulationtype, and data rate at a maximum of PA efficiency. Of course, only thoserequirements specified or deemed essential need be considered. Of note,in some systems fewer or more requirements are specified. This method isillustrated in FIG. 1 a for the apparatus of FIG. 1 b.

Alternatively, analogue control signals are used, for example, a controlsignal is provided for each controllable aspect of the amplifieroperation.

Alternatively, the information on EVM, mask, channel to be used, maximumallowable power output level, modulation type, and data rate is providedto the PA and the mapping to the appropriate operating point for one ormore amplification stages and/or matching circuit adjustments for one ormore of the interstage/output match circuits is determined andcontrolled internally to the integrated PA circuit. In either case, PAefficiency is improvable even in consideration of many operating factorsand requirements.

For example, according to an embodiment with a multi-carrier OFDMmodulation, the operating point of the amplifying transistors and/or theinterstage matching circuit is adjusted for lower or higher powerefficiency in a circumstance where:

-   -   the channel selected to be employed in a transmission system is        close to a band edge. For example, in the US, the 2.4 GHz WLAN        band ranges from 2400-2483.5 MHz. Typical operating channels        include channel 1 (2412 MHz), 6 (2437 MHz), and 11 (2462 MHz).        The FCC has defined so-called restricted bands of operation        where emissions must be lower than a predefined limit to protect        devices operating in these bands. For example, there is a        restricted band from 2300-2390 MHz, and another from 2483.5 MHz        to 2500 MHz. These restricted bands form a band-edge, and put        strict limits on how much power can be radiated into these        bands. If the PA is operating on channel 1 or 11, it is obvious        that the restricted band is quite close to the operating        frequency of the PA (22 MHz below channel 1, and 21.5 MHz above        channel 11). However, if the PA is operating in channel 6, the        restricted band is now greater than 45 MHz away. Out-of-band        emissions from a power amplifier are directly related to PA        linearity, so a PA operating in channels 1 or 11 is often        required to be more linear than one operating in channel 6.        Thus, changing the biasing and/or matching characteristics of        the amplifier when operating in channel 1 or 11 is advantageous        because efficiency is improvable for a relatively common        situation.    -   a data rate to be employed is lower or higher and        correspondingly requires less or more linear performance from        the PA,    -   the type of modulation to be employed requires a less or more        linear performance from the PA (eg. QPSK, BPSK, QAM 16, etc.)    -   the jurisdiction in which the PA is to be compliant requires        more or less linear power output from the PA to meet its        standards,    -   an evaluation of mask compliance and EVM performance indicates        that an increase or decrease in linear performance or power        level is required, and    -   the channel bandwidth is variable and therefore requires more or        less linear performance from the PA.

For many WLAN applications, currents can be reduced by 25%. Furtherenhancements in WLAN applications occur at or near the band edge wherebias is approximately optimized to increase transmit power. Further, forlower data rates, less current is required and, as such, when lower datarate transmission is used power savings are supported. It isadvantageous to adjust the bias current in a fashion that does notprevent meeting of other requirements of the system such as EVM.

Of course, in today's world of international travel and business, oftena single mobile communication device is intended to operate in manycountries. As such, the ability to meet performance characteristics indifferent jurisdictions efficiently is highly advantageous. Similarly,the other situations also present advantages to enhancing efficiency ofoperation when possible.

Preferably, power consumption is approximately minimized in a PA byadjusting of one or more operating points in amplification stages of thePA. Alternatively or in conjunction therewith, the matching circuits ofthe PA are adjusted. Such a method is useful for balancing differentrequirements. For example, it supports minimum simultaneous requirementsof power output, absolute and relative spectral output outside anallowed frequency bands (mask), and EVM. In particular, in the contextof an EVM limited transmission system, if the modulation rate isreduced, the power consumption is reduceable using an adjustment in theoperating point and optionally an adjustment in the matching circuits toreduce the level of back-off while still meeting mask requirements andthe EVM requirement. In other cases, competing requirements are balancedusing dynamic alterations to the amplifier circuit as taughthereinabove.

In a more specific embodiment, an extremely critical performance metricof a WLAN Power Amplifier is EVM performance. To meet System EVMperformance requirements, power amplifiers are typically specified to 3%EVM performance from the PA at the rated transmit power. Thisspecification leaves some margin for the total system EVM. Referring toFIG. 2 a, a diagram of EVM(%) vs. P_(out) (dBm) is shown. As is evidentfrom the graph, the EVM of 3% as discussed herein is a horizontal dashedline but the mask is only an approximation thereof several dB below thethreshold to provide additional margin. At low P_(out), the margin isapproximately 20 dB whereas as P_(out) increases, the margin shrinks toabout 6 dB. Because of the high peak to average power of OFDMmodulation, power amplifier power is reduced significantly from the 1 dBcompression point to meet the 3% EVM requirement. As noted hereinabove,reducing the PA output power results in poor PA efficiency when the PAis actually operated at the lower power level. In fact, Mask complianceat the 3% EVM level has several dB of margin, which makes the system“EVM limited” as seen in FIG. 2 a where the threshold of 3% EVM iscrossed by the 54 Mbps EVM curve much before the Mask (spectral energy)threshold with increasing power output level (P_(out)). Though lowermodulation rates reduce the EVM requirement and therefore support alower bias setting which improves efficiency and extends product batterylife, these are not always available or used.

When optimizing EVM performance, particular care is given to biasing acircuit for efficiency of operation at the EVM performance.Consideration of EVM at lower power levels or “backed off” EVMperformance is taken into consideration to not exceed a givenspecification. Typically, lower bias results in increased backed-offEVM, commonly referred to as EVM “humping.” This is illustrated in FIG.2 b where EVM at a lower bias point crosses the 3% threshold briefly atapproximately 16 dBm power output and then the EVM crosses the thresholdagain at 20 dBm. This lower power operating point correspondinglyresults, in a lower ICC consumption (power consumption) over the fullrange of output powers (see FIG. 3). As such, it is desirable, butproblematic.

According to an embodiment of the invention, bias at each power level isadjusted to approximately optimize EVM and efficiency for betterperformance. This results in a dramatic improvement in overall PAperformance. FIGS. 4 and 5 show the approximately optimized performanceof a PA with digital bias control set for EVM and efficiency. There is asubstantial improvement in current drain by dynamically controlling biasat each power level to meet the EVM requirements with a minimum currentconsumption performance. Advantageously, such a system reduces theoverall power consumption, thereby increasing battery life, whilemaintaining other performance characteristics of the PA.

Some applications allow for higher transmit power levels at lowermodulation rates, where the performance is mask limited instead of EVMlimited. Dynamic bias control allows for further increasing transmitpower or improving efficiency by approximately re-optimizing poweramplifier bias for approximately optimum spectral mask performance.Referring to FIG. 6, shown is an EVM vs. bias current graph whereinefficiency of operation is determinable. As is evident from the graph,the bias current is reduceable from 170 to 150 mA, improving theefficiency from 17% to 20%. By dynamically adjusting operating points inresponse to operation of the PA, efficiency is improved whilemaintaining performance within requirements.

Band edge requirements are taken from the FCC restricted band limits,outlined in the FCC Part 15.205 specification, along with the radiatedemission limits defined in FCC Part 15.209. Meeting the FCC Band Edgerequirements typically requires setting lower transmit power levels atchannels 1 and 11 (2412 MHz and 2462 MHz). Typically, power at the bandedge channels—1 and 11—is 3 to 4 dB lower than that of channels that arenot band edge limited. As noted above, this results in reducedefficiency of operation.

As can be seen in FIGS. 7, 8, and 9, increasing PA bias current greatlyimproves Band Edge performance (or Out Of Band—OOB) for 802.11b and802.11g Band Edge performance. In FIG. 7, the performance improvementwith the lower bias current is evident. Here, not only is the specifiedlimit crossed at a higher power level, the OOB is lower and moreconsistent across the entire range where the higher bias currentoperation is within the specified limit. This allows for increasedamplification when desired. From these plots it is evident that thetransmit power can be increased up to 3 dB for 802.11b and 1.5 dB for802.11g signals at the band edge channels by appropriately adjusting thepower amplifier bias.

In an alternative embodiment, a bias of the PA is adjusted in a discretestepwise fashion. Referring to FIG. 10, an impact of using only 2 biaspoints with a single transition is shown. Icq is reduced from 250 mA to128 mA, and power consumption is reduced. This provides some of thebenefits outlined hereinabove but with a much simpler implementation.For example, 2-step control could be implemented using a separatecontrol pin. Alternatively, a serial interface is used allowing reducedcomplexity as the number of bias points is increased. As shown in FIG.11, EVM remains below 3% over the entire power range and the single biaschange improves efficiency within one of the two ranges. In the exampleshown, there is a step discontinuity in EVM at 17 dBm. Of course, theswitch point could be lowered if EVM<2% is required at backed-offpowers.

Alternatively, more than two bias points are used.

In another alternative embodiment, a fixed bias point is used over oneor more ranges while a variable bias point is used over one or moreother ranges. Thus, the benefits of the simplicity of the embodiment ofFIGS. 10 and 11 are achieved with the improved EVM behavior of the firstembodiment over the ranges specified.

Referring to FIG. 12 a, a method is shown wherein a control signal isreceived for selectively switching the amplifier between a first biasingmode of operation with reduced current and a second other biasing modeof operation with higher bias current. For example, the control signalis provided at a pin wherein a “0” indicates low bias current and a “1”indicates higher bias current. Alternatively, the signal is providedwithin a digital control signal comprising other control values.Referring to FIG. 12 b, an amplifier circuit is shown for use with themethod of FIG. 12 a.

Advantageously, using CMOS technology within a SiGe BiCMOS technologyallows for digital control of an amplifier according to embodiments ofthe present invention. The use of a digital control and interface for acontrol signal presents several advantages. Firstly, the control signaloptionally comprises a digital selection of two or more amplifierconfigurations. For example, those shown in FIG. 12 a. Using a digitalcontrol signal is advantageous as it allows N different amplifierconfigurations to be selectable without requiring numerous input portsor pins. Secondly, it allows for the amplifier to select an amplifierconfiguration based on data provided in a simple form which can, withlittle further processing, be used in the configuration of theamplifier. For example, the control signal comprises an indication of astandard, a channel, a modulation type and rate, etc. and the amplifierintegrated circuit comprises logic for mapping those values onto alookup table to determine a configuration. Alternatively, the values areprocessed to determine a configuration of the amplifier supportingcontinuous variation of biasing and/or matching circuits. Of course, itis also supported that a lookup table establishes the processing to beperformed in order to support continuous variation of biasing and/ormatching circuits.

Within the amplifier, bias is controllable. Also within the amplifier,filters can be designed in a fashion to provide controllability. Thesetunable filters are useful in that better filtering—higherrejection—usually has an associated higher insertion loss. As such, anability to tune a filter to reduce rejection would also advantageouslyreduce insertion loss. Filter tuning is useful in improving efficiencyin some applications.

In some embodiments, digital control, which supports separate controlover each tunable aspect of an amplifier is provided. This optionallyincludes each stage of the amplifier as well. As such, bias iscontrollable for each amplifier stage and filters are tunableindependently for each amplification stage. By providing independentcontrol, a control that results in an approximately most efficientoperation of the amplifier is selectable. This also adds significantflexibility in the event of new standards and new modulation techniques.

Optionally only some of the stages are independently controllable.Further optionally, each stage receives a same control signal.

In an alternative embodiment, the matching circuits are controlledinstead of the bias current in order to achieve similar benefits. In yetanother embodiment, the bias current and matching circuits arecontrolled. For example, the bias point of the PA is adjusted and thenthe matching circuit is adjusted to account for any changes in the PAload line. Of course, as will be evident to those of skill in the art,other methods of achieving control over biasing of the PA and/or controlover the matching circuits are also applicable to embodiments of theinvention.

Though the invention has been described with reference to a set ofpotential variables for use in tuning of the amplifier, any one or moreof those variables is independently useful for amplifier control oruseful in conjunction with one or more other variables. For example,channel bandwidth is useful in isolation or with modulation type, forexample. Similarly, each is useful with more than one other variable orin isolation.

Numerous other embodiments may be envisaged without departing from thescope of the invention.

1. An amplifier circuit comprising: an amplifying transistor configuredto receive an input RF signal, provide an output amplified RF signal,and receive a first bias current; and a control circuit configured todetermine the first bias current for the amplifying transistor dependentupon an error vector magnitude (EVM) target, an operating point, and anoperating channel of the amplifier circuit, and to provide the firstbias current to the amplifying transistor through a control signal, thefirst bias current being different for channels at an edge of a channelband than for channels nearer a center of the channel band, the firstbias current being determined for to improve an amplifier efficiency ofoperation relative to that of an amplifying transistor with a fixed biascurrent.
 2. The amplifier circuit of claim 1 wherein the first biascurrent is selected from a plurality of discrete bias currents, each ofthe discrete bias currents being selected for a different range ofoperation of the amplifying transistor.
 3. The amplifier circuit ofclaim 1 wherein the control signal adjusts a gain of the amplifyingtransistor to enhance the amplifier efficiency of operation whilemaintaining at least a predetermined EVM.
 4. The amplifier circuit ofclaim 3 wherein adjusting is performed along a continuous response ofburst current versus output power.
 5. The amplifier circuit of claim 3wherein adjusting is performed along a discontinuous response of burstcurrent versus output power, discontinuities in the discontinuousresponse representing changes in bias.
 6. The amplifier circuit of claim1 wherein the control signal is varied dependent upon at least one ofmodulation type and modulation rate.
 7. The amplifier circuit of claim 6wherein the control signal adjusts a gain of the amplifying transistorto enhance the amplifier efficiency of operation while providing themodulation type and rate.
 8. The amplifier circuit of claim 7 whereinthe control signal adjusts the gain of the amplifying transistor tomaintain the EVM at a value better than the EVM target while providingthe modulation type and rate.
 9. The amplifier circuit of claim 1wherein the control signal includes a digital control signal.